1. Field of the Invention
The present invention relates to a control valve for controlling the discharging capacity of a variable displacement compressor.
2. Description of the Related Art
An automotive air conditioner is generally configured by arranging and placing a compressor, a condenser, an expander, an evaporator, and so forth in a refrigeration cycle. The compressor is, for example, a variable displacement compressor (hereinafter referred to simply as “compressor” also) capable of varying the refrigerant discharging capacity in order to maintain a constant level of cooling capacity irrespective of the engine speed. In this compressor, a piston for compression is linked to a wobble plate, which is mounted to a rotational shaft rotatingly driven by an engine. And the refrigerant discharging rate is regulated by changing the stroke of the piston through changes in the angle of the wobble plate. The angle of the wobble plate is changed continuously by changing the balance of pressure working on both faces of the piston as part of the discharged refrigerant is introduced into a hermetically-closed crankcase. The pressure within this crankcase (hereinafter referred to as “crank pressure”) Pc is controlled by a control valve for a variable displacement compressor (hereinafter referred to simply as “control valve” also), which is provided between the discharge chamber and the crankcase of the compressor.
Such a control valve is often configured as an electromagnetic valve and has a valve hole, through which to communicate between the discharge chamber and the crankcase, within a body. And the opening degree of a valve section is regulated by moving a valve element, placed within the body, toward and away from the valve hole, thereby controlling the flow rate of refrigerant introduced into the crankcase. The valve opening degree is regulated by a balance among a force, generated by a refrigerant pressure, acting on the valve element, a drive force generated by a solenoid, and a biasing force of a spring placed for the purpose of regulating a control setting value.